The alkaline-earth metal halophosphate phosphor is the most widely used luminescent material. This composition is described in U.S. Pat. No. 2,488,733, issued Nov. 22, 1949. The halophosphate phosphor is the standard phosphor used in fluorescent lamps, and it is activated by antimony or antimony plus manganese. This phosphor has the crystalline structure of the naturally occurring mineral apatite, which is a hexagonal crystal structure. This matrix of material is generally expressed as: EQU 3M.sub.3 (PO.sub.4).sub.2.M(X).sub.2 or as M.sub.5 (PO.sub.4).sub.3 X,
where M is one or more of the alkaline-earth metals, and X is one or more of the halogens, and generally a fluorine-chlorine mixture. This material is also referred to as apatite structured halophosphate phosphor.
Recent attention in phosphor developments have turned to preparing phosphors which efficiently produce visible light of a narrow bandwidth at a characteristic wavelength when excited by ultraviolet radiation. The characteristic bandwidth is usually referred to as half-width, and is determined by measuring the bandwidth at an emission intensity which is one-half the maximum or peak emission intensity. The rare-earth metals are known to be useful in producing line-emitting, or narrowband-emitting phosphors with various matrices.
Various trivalent rare-earth metals such as terbium and cerium having been added in small amounts to halophosphate compositions to improve phosphor efficiency. Divalent europium is known as an efficient and useful activator with various phosphate compositions.